Transmitter

ABSTRACT

To provide a transmitter wherein even in a case of sharing a detector circuit between or among a plurality of transmitting circuits, a high degree of detection accuracy can be achieved without increasing the signal power supplied to the detector circuit. In a transmitter including a detector circuit shared by transmitting circuits and that deal with signals of different frequency bands, a capacitor C 1 , which constitutes an RF coupler disposed on an output signal line of the transmitting circuit, is directly connected to the input terminal of the detector circuit, while series coils L 1  and L 2  are inserted between a capacitor C 2 , which makes up an RF coupler disposed on an output signal line of the transmitting circuit which deals with signals of a lower frequency band than the transmitting circuit, and the input terminal of the detector circuit.

REFERENCE TO RELATED APPLICATION

This is a continuation application of U.S. patent application Ser. No.12/375,664 filed Jan. 29, 2009 and claims the benefit of its priority.

TECHNICAL FIELD

The present invention relates to a transmitter, and more specifically toa transmitter wherein a detector circuit is shared among a plurality oftransmitting circuits that deal with signals of different frequencybands.

BACKGROUND ART

FIG. 6 is a diagram showing an example of a formulation of aconventional transmitter in case of having only one transmittingcircuit. In FIG. 6, the conventional transmitter comprises a GCA (GainControl Amplifier) 11 which makes up a transmitting circuit 1, a PA(Power Amplifier) 12 which makes up the transmitting circuit 1, an RF(Radio Frequency) coupler 13, a detector circuit 14; a reference voltagegenerator 15, a comparator 16, and an integrating circuit 17. FIG. 7 isa diagram showing a structure of the detector circuit 14 in FIG. 6. Thedetector circuit 14 comprises a diode unit 14-1 and a LPF (Low-PassFilter) 14-2. The detector circuit 14 may comprise a detector IC insteadof the diode unit.

The GCA 11 is an amplifier whose gain can be variably controlled by anexternal analog voltage. The PA 12 is an amplifier disposed at the finalstage of the transmitting circuit; and it has a constant gain. The RFcoupler 13 branches a radio frequency signal power output from the PA 12and supplies part of the power to the detector circuit 14. The detectorcircuit 14 detects the branched radio frequency signal power and outputsit as a detection signal. The detection voltage should be higher by acertain level than the noise floor to improve its error estimationaccuracy. The comparator 16 compares the detection voltage with areference voltage VRef of a target transmission power generated by thereference voltage generator 15 and outputs a difference voltage. Thedifference voltage is integrated by the integrating circuit 17 and inputto the GCA 11 as a feedback; therefore, the gain of the GCA 11 isvariably controlled.

A high accuracy in the power detection is required for the detectorcircuit 14, because the circuit 14 is used for the purpose ofcontrolling the output power of the transmitting circuit accuratelytoward a predetermined value. Therefore, the output voltage (detectionvoltage) of the detector circuit 14 should be high enough above thenoise floor level.

In general, if there is provided a plurality of transmitting circuitseach deals with different frequency bands, a detector circuit isequipped for each of the transmitting circuits. FIG. 8 is a diagramshowing a formulation of a conventional transmitter with twotransmitting circuits, wherein an equivalent component with that in FIG.6 is indicated by an identical reference numeral. As well as thecomponents in FIG. 6, the transmitter shown in FIG. 8 further comprisesa GCA 21 which makes up a transmitting circuit 2, a PA 22 which makes upthe transmitting circuit 2, an RF coupler 23 for branching a radiofrequency signal power output from the PA 22 and supplying part of thepower to a detector circuit 24, and a detector circuit 24 for detectingthe branched radio frequency signal power output. A structure of thedetector circuit 24 is similar to that in the detector circuit 14 shownin FIG. 7.

The transmitting circuit 1 and the transmitting circuit 2 are operatedexclusively to each other; while one is in operation, the other isstopped. For example, the transmitting circuit 1 deals with signals of aradio frequency band (for example, 2 GHz band); and the transmittingcircuit 2 deals with signals of a low frequency band (for example, 800MHz band).

In this case, since the detector circuit in one transmitting circuit isindependent from the detector circuit in the other transmitting circuit,interference between the detector circuit 14 and 24 does not occur and adetection voltage which is higher than a certain level is easilygenerated. However, since a plurality of detector circuits is required,there is a disadvantage from viewpoints of cost and mounting area.

FIG. 9 is a diagram showing another structure of a conventionaltransmitter with two transmitting circuits, wherein an equivalentcomponent with that in FIG. 8 is indicated by an identical referencenumeral. The transmitter shown in FIG. 9 is different from that shown inFIG. 8 in that, by sharing the detector circuit 14 between thetransmitting circuits 1 and 2, the detector circuit 24 is removed. Whena detector circuit is shared among a plurality of transmitting circuitsin this way, there is an advantage that cost and mounting area arereduced compared with the formulation shown in FIG. 8.

For example, Patent Document 1 describes a formulation wherein adetector circuit is shared among a plurality of transmitting circuits.

[Patent Document 1]

-   JP Patent Kokai Publication No. JP-P2006-080810A

[Patent Document 2]

-   JP Patent Kokai Publication No. JP-P2003-046408A

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The disclosures of the Patent Documents 1 and 2 above are incorporatedherein by reference thereto. The following analysis of the related artis given by the present invention. In the formulation shown in FIG. 9,interference between the transmitting circuits 1 and 2 occurs and thedetection sensitivity changes depending on frequencies. Moreover, thesensitivity is decreased due to leakage power for detection into atransmitting circuit for the other frequency band. Therefore, to realizea minimum detection voltage at the same level with the case where thedetector circuit is not shared, it is necessary to increase the radiofrequency signal power supplied to the detector circuit. As a result, itis necessary to increase an output power from the PA and the GCA; andthere occurs a problem that current consumption increases.

Patent Document 2 describes a formulation, wherein transmitting signalsfrom transmitting units TX1 and TX2 which deal with signals of differentfrequency bands are merged at a diplexer unit which comprises a LPF anda HPF (High Pass Filter) and transmitted to a common antenna. Thisformulation prevents the transmitting signal from leaking into anothertransmitting unit; however, the formulation increases the number of thecomponents.

It is an object of the present invention to provide a transmitterwherein even in a case of sharing a detector circuit between or among aplurality of transmitting circuits, a high detection accuracy can beachieved without increasing the signal power supplied to the detectorcircuit.

Means to Solve the Problems

According to a first aspect of the present invention, there is provideda transmitter comprising: a first transmitting circuit which correspondsto a signal of a first frequency band; a second transmitting circuitwhich corresponds to a signal of a second frequency band having a lowerfrequency band than the first frequency band; a first coupler which,disposed on an output signal line of the first transmitting circuit,branches and outputs part of an output signal from the firsttransmitting circuit; a second coupler which, disposed on an output lineof the second transmitting circuit, branches and outputs part of anoutput signal from the second transmitting circuit; and a detectorcircuit detecting an input signal whose input terminal is coupled to abranched output terminal of the first coupler and a branched outputterminal of the second coupler, wherein the input terminal is directlyconnected to the branched output terminal of the first coupler; and afilter circuit which, arranged between the input terminal and thebranched output terminal of the second coupler, selectively passes asignal of the second frequency band.

In the above transmitter, the filter circuit may be a series of coils(inductors) arranged between the input terminal and the branched outputterminal of the second coupler.

In the above transmitter, the first coupler may be a first capacitorwhose first terminal is coupled to a output signal line of the firsttransmitting circuit and second terminal is coupled to the inputterminal; the second coupler may be a second capacitor whose firstterminal is connected to an output signal line of the secondtransmitting circuit; a first coil of the coils, whose first terminal isconnected to the input terminal, may be disposed near the firstcapacitor; and a second coil of the coils, whose first terminal isconnected to a second terminal of the first coil and second terminal isconnected to a second terminal of the second capacitor, may be disposednear the second capacitor.

In the above transmitter, the coil may be substituted by a capacitor.

The above transmitter may further comprise: a third transmitting circuitwhich corresponds to signals of a third frequency band having a lowerfrequency band than the second frequency band; and a third couplerwhich, disposed on an output signal line of the third transmittingcircuit, branches and outputs part of an output signal from the thirdtransmitting circuit, wherein a filter circuit which, arranged betweenthe input terminal and a branched output terminal of the third coupler,selectively passes a signal of the third frequency band.

According to a second aspect of the present invention, there is provideda transmitter comprising: a first transmitting circuit which correspondsto a signal of a first frequency band; a second transmitting circuitwhich corresponds to a signal of a second frequency band having a lowerfrequency band than the first frequency band; a first coupler which,disposed on an output signal line of the first transmitting circuit,branches and outputs part of an output signal from the firsttransmitting circuit; a second coupler which, disposed on an output lineof the second transmitting circuit, branches and outputs part of anoutput signal from the second transmitting circuit; and a detectorcircuit detecting an input signal whose input terminal is coupled to abranched output terminal of the first coupler and a branched outputterminal of the second coupler, wherein the input terminal is directlyconnected to the branched output terminal of the first coupler; and aphase shifter, providing a signal of the first frequency band with alarger phase shift than that for a signal of the second frequency band,is arranged between the input terminal and the branched output terminalof the second coupler.

The above transmitter may further comprise a controller which variablycontrols a gain of a variable gain amplifier in the first transmittingcircuit based on a detection output of the detector circuit while thefirst transmitting circuit is operated and variably controls a gain of avariable gain amplifier in the second transmitting circuit based on adetection output of the detector circuit while the second transmittingcircuit is operated.

In this way, according to the present invention, in a transmitterincluding a detector circuit shared by a first transmitting circuit anda second transmitting circuit, a branched output terminal of a firstcoupler disposed on an output signal line of the first transmittingcircuit is directly connected to an input terminal of a detectorcircuit; and a filter circuit or a phase shifter is arranged between abranched output terminal of a second coupler disposed on an outputsignal line of the second transmitting circuit which deals with signalsof the lower frequency band than the first transmitting circuit, and theinput terminal of the detector circuit.

According to a third aspect of the present invention, there is provideda transmitter comprising: a first transmitting circuit which correspondsto a signal of a first frequency band; a second transmitting circuitwhich corresponds to a signal of a second frequency band having a lowerfrequency band than the first frequency band; a detector circuit whichdetects an input signal; a first coupler which, disposed on an outputsignal line of the first transmitting circuit, branches and outputs partof an output signal from the first transmitting circuit to the detectorcircuit; and a second coupler which, disposed on an output line of thesecond transmitting circuit, branches and outputs part of an outputsignal from the second transmitting circuit to the detector circuit; andthe transmitter further comprising, between the second coupler and thedetector circuit, one of a filter circuit which selectively passes asignal of the second frequency band and a phase shifter which provides asignal of the first frequency band with a larger phase shift than thatfor a signal of the second frequency band.

The above transmitter may further comprise: a third transmitting circuitwhich corresponds to signals of a third frequency band having a lowerfrequency band than the second frequency band; and a third coupler whichbranches part of an output signal of the third transmitting circuit inan output signal line of the third transmitting circuit and outputs thepart to the detector circuit, and a second filter circuit which,arranged between the second coupler and the detector circuit,selectively passes a signal of the third frequency band.

In the above transmitter, both of the filter circuits may be a coil orseries coils.

In the above transmitter, both of the filter circuits may be acapacitor.

In the above transmitter, both of the first coupler and the secondcoupler may be a capacitor.

The above transmitter may further comprise a controller which variablycontrols a gain of a variable amplifier in the first transmittingcircuit based on a detection output of the detector circuit while thefirst transmitting circuit operates and variably controls a gain of avariable gain amplifier in the second transmitting circuit based on adetection output of the detector circuit while the second transmittingcircuit operates.

Meritorious Effects of the Invention

According to the present invention, in a transmitter including adetector circuit shared by a first transmitting circuit and a secondtransmitting circuit, to reduce the power loss, a filter circuit or aphase shifter is arranged between a branched output terminal of a secondcoupler disposed on an output signal line of the second transmittingcircuit which deals with signals of the lower frequency band than thefirst transmitting circuit and an input terminal of the detectorcircuit. Therefore, there is provided an advantage that even in a caseof sharing a detector circuit between or among a plurality oftransmitting circuits, a high degree of detection accuracy can beachieved without increasing the signal power supplied to the detectorcircuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram showing a formulation of a conventional transmitterto illustrate a first mode of the present invention. FIG. 1B is adiagram showing a formulation of a transmitter according to the firstmode of the present invention.

FIG. 2 is a diagram showing an arrangement of capacitors and coils inthe transmitter of FIG. 1B.

FIG. 3A is a diagram showing a simulation result of relationship betweena distance ‘a’ and a detection voltage, where ‘a’ denotes a distancebetween a capacitor and an coil. FIG. 3B is a diagram showing asimulation result of relationship between a distance ‘b’ and a detectionvoltage, where ‘b’ denotes a distance between coils.

FIG. 4 is diagram showing a formulation of a transmitter according to asecond mode of the present invention.

FIG. 5 is a diagram showing a formulation of transmitter according to athird mode of the present invention.

FIG. 6 is a diagram showing a formulation of a conventional transmitterwith a single transmitting circuit.

FIG. 7 is a diagram showing a formulation of the detector circuit inFIG. 6.

FIG. 8 is a diagram showing a formulation of a conventional transmitterwith two transmitting circuits.

FIG. 9 is a diagram showing another formulation of a conventionaltransmitter with two transmitting circuits.

EXPLANATIONS OF SYMBOLS

-   1, 2, 3 Transmitting circuit-   11, 21 GCA (Gain Control Amplifier)-   12, 22, 32 PA (Power Amplifier)-   13 RF coupler-   14 Detector circuit-   14-1 Diode unit-   14-2 LPF (Low-Pass Filter)-   15 Reference voltage generator-   16 Comparator-   17 Integrating circuit-   101 Phase shifter-   C1, C2, C3 Capacitor-   L1, L2, L3, L4 Coil

PREFERRED MODES FOR CARRYING OUT THE INVENTION

In the following, a preferred mode of the present invention is describedwith reference to the drawings.

FIG. 1A is a diagram showing a formulation of a conventional transmitterfor illustrating a first mode of the present invention. FIG. 1B is adiagram showing a formulation of a transmitter according to the firstmode of the present invention, where an equivalent component with thatin FIG. 9 is indicated by an identical reference numeral.

In FIGS. 1A and 1B, the transmitting circuit 1 and the transmittingcircuit 2 are operated exclusively to each other; while one is inoperation, the other is stopped. For example, the transmitting circuit 1deals with signals of a frequency band (for example 2 GHz band); and thetransmitting circuit 2 deals with signals of a low frequency band (forexample, 800 MHz band).

With reference to FIG. 1A, a formulation of a transmitter is shown,which employs, as an RF coupler 13 in FIG. 9, a capacitor C1 whose firstterminal is connected to an output signal line of the first transmittingcircuit 1 and second terminal is connected to an input terminal of adetector circuit 14 and employs, as an RF coupler 23 in FIG. 9, acapacitor C2 whose first terminal is connected to an output signal lineof the transmitting circuit 2 and second terminal is coupled to anoutput terminal of the detector circuit 14.

A frequency of signals (signal 1) for the transmitting circuit 1 isdenoted by f1 and a frequency of signals (signal 2) for the transmittingcircuit 2 is denoted by f2. Now it is assumed that f1=2*f2.

If it is assumed that sensitivity and an input impedance of the detectorcircuit 14 for f1 are the same with those for f2, a power in thetransmitting circuit 1 required for the detector circuit 14 to achieve adetection voltage is the same with that in the transmitting circuit 2.Therefore, an impedance of C1 at f1 is the same with that of C2 at f2.

An impedance Z of a capacitor with capacitance C at a frequency f can becalculated based on the following equation (1)

Z=1/(2π*f*C)  (1)

Therefore, an impedance Z1 of C1 at the frequency f1 is given by

Z1=1/(2π*f1*C1)  (2)

and an impedance Z2 of C2 at the frequency f2 is given by

Z2=1/(2π*f2*C2)  (3).

Moreover, since f1=2*f2, the relation between C1 and C2 is given by2*C1=C2.

Therefore, an impedance Z12 of C2 at the frequency f1 is given by

Z12=Z1/2  (4)

and an impedance Z21 of C1 at the frequency f2 is given by

Z21=2*Z2  (5).

In general, when a plurality of loads is connected in parallel to asignal source, a power distributed to a load with a lower impedance ishigher than that distributed to a load with a higher impedance.

Based on the above consequence, since an impedance of C2 is low for asignal from the transmitting circuit 1, the signal easily leaks into thetransmitting circuit 2 via C2 and an input to the detector circuit 14decreases. On the other hand, impedance of C1 is high for a signal fromthe transmitting circuit 2, the signal barely leaks into thetransmitting circuit 1 and an input to the detector circuit 14 does notdecrease. In the formulation shown in FIG. 1A, it is easy to generate adetection voltage, which is higher than a certain level, of thetransmitting circuit 2 for lower frequencies; however it is difficult togenerate a detection voltage of the transmitting circuit 1 for higherfrequencies.

Therefore, the leakage power should be reduced by forming a LPF circuitor a BPF (Band Pass Filter) circuit, between the capacitor C2 and theinput terminal of the detector circuit 14, which selectively passes asignal of the frequency band for the transmitting circuit 2.

In the first mode of the present invention, a coil L1 and a coil L2 areinserted in series between the capacitor C2 and the input terminal ofthe detector circuit 14 as shown in FIG. 1B to increase the impedanceand reduce the leakage power. The number of coils may be one. However,insertion of two coils allows a fine adjustment of the parameter.

The coil L1 is disposed near the capacitor C1 and the coil L2 isdisposed near the capacitor C2 to prevent attenuation of output signalsof the transmitting circuits due to formation of an unintentional stubin the pattern on the board. FIG. 2 is a diagram showing an arrangementof the coils L1, L2 and the capacitors C1, C2 in the transmitter in FIG.1B. The coils L1, L2 and the capacitors C1, C2 are shown as a chipcomponent whose striped area is a terminal of the chip component.

As shown in FIG. 3A, the detection voltage decreases significantlydepending on the distance a, when the coils L1 and L2 cannot bearranged, respectively, near the capacitors C1 and C2. On the otherhand, as shown in FIG. 3B, the detection voltage does not decreasesubstantially, even when the distance b between the two coils L1 and L2is increased.

The number of inserted coils may be only one as described above. In thiscase, the coil is arranged near one of the capacitors C1 and C2. Thenumber of inserted coils may be three or more. In this case, the coilsL1 and L2 are arranged, respectively, near the capacitors C1 and C2 asdescribed above and the other coil is arranged between these coils L1and L2.

Moreover, a capacitor can be inserted instead of the coils. Although thecapacitors C1 and C2 are employed as the RF couplers 13 and 23, adirectional coupler without a capacitor can also be employed.

As described above, in the first mode of the present invention, thepower loss is decreased by connecting series coils between the RFcoupler which is disposed on an output signal line of the transmittingcircuit 2 and an input terminal of the detector circuit 14. Therefore,even when the detection circuit 14 is shared, a detection voltage higherthan a certain level can be generated and a high degree of detectionaccuracy can be achieved by suppressing variation of the detectionsensitivity which depends on the frequency.

Since it is not necessary to increase the coupling at the RF coupler,low current consumption is realized without increasing currentconsumption in the PA and the GCA, even when the detector circuit isshared.

A Second Mode

Next, a second mode of the present invention is explained. FIG. 4 is adiagram showing a formulation of a transmitter according to the secondmode of the present invention, wherein an equivalent component with thatin FIG. 1 is indicated by an identical reference numeral.

As shown in FIG. 4, a transmitter according to the second mode of thepresent invention is different from that in the first mode of thepresent invention shown in FIG. 1B in that a phase shifter whichcomprises, for example, L, C and R is disposed between a capacitor C2and an input terminal of a detector circuit 14 instead of the coils L1and L2.

A phase shifter shifts the phase of signals. The amount of phase shiftby an identical phase shifter varies depending on the frequency. Forexample, a phase shifter which shifts a phase of signals of frequency f1by 90 degrees shifts a phase of signals of frequency 2*f1 by 180degrees.

In FIG. 4, a phase shifter 101 is arranged between a capacitor C2 and aninput terminal of a detector circuit 14. Insertion of the phase shifter101 allows a large phase shift of signals of the transmitting circuit 1side while preventing a large phase shift of signals of the transmittingcircuit 2 side which deals with lower frequency signals. The amount ofthe phase shirt of the phase shifter 101 is adjusted to a state wherethe impedance of the transmitting circuit 2 side for signals of thetransmitting circuit 1 side can be regarded as nearly open.

This adjustment prevents leakage of transmitting signal power from thetransmitting circuit 1 to the transmitting circuit 2 side and increasespower supplied to the detector circuit 14. Therefore, a detectionvoltage for the transmitting circuit 1 side, which is higher than acertain level, is generated.

Although the capacitors C1 and C2 are employed as the RF couplers 13 and23, a directional coupler without a capacitor may also be employed. Achip component may be employed as L, C and R composing the phaseshifter. Moreover, the wire length between the capacitor C2 and theinput terminal of the detector circuit 14 can be elaborated.

Next, a third mode of the present invention is illustrated. FIG. 5 is adiagram showing a structure of a transmitter according to a third modeof the present invention, where an equivalent component with that inFIG. 1 is indicated by an identical reference numeral.

As shown in FIG. 5, a transmitter according to the third mode of thepresent invention is different from that in the first mode of thepresent invention shown in FIG. 1B in that a transmitting circuit 3dealing with signal of frequency f3 is composed in addition to atransmitting circuit 2 which deals with signals of frequency f1 and atransmitting circuit 3 which deals with signals of frequency f2. It isassumed that a relation f1>f2>f3 holds among these frequencies. Thetransmitting circuits 1, 2 and 3 operate exclusively to be another;while one of them is in operation, the others are stopped.

A GCA 11, a GCA 21, a reference voltage generator 15, a comparator 16and an integrating circuit 17 shown in FIG. 1B are abbreviated in FIG.5. It goes without saying that the transmitting circuit 3 comprises aGCA in addition to the PA 32 in the same way as the transmittingcircuits 1 and 2 do; and the gain of the GCA in the transmitting circuit3 is also controlled by an output from the integrating circuit 17 whilethe transmitting circuit 3 is in operation.

In FIG. 5, a capacitor C3 is employed as an RF coupler which is disposedon the output signal line of the transmitting circuit 3 and coils L3 andL4 are inserted in series between the capacitor C3 and an input terminalof the detector circuit 14. The coils L1 and L2 work as a BPF circuitwhich passes signals of a frequency band for the transmitting circuit 2;and the coils L3 and L4 works as a LPF circuit which passes signals of afrequency band for the transmitting circuit 3.

Here, the coils L3 and L4 are arranged, respectively, near thecapacitors C1 and C3 in the same way as the coils L1 and L3 as describedabove with reference to FIG. 2.

The number of coils inserted between the capacitor C3 and the inputterminal of the detector circuit 14 may be only one. In this case, thecoil is arranged near one of the capacitors C1 and C3. The number ofcoils inserted between the capacitor C3 and the input terminal of thedetector circuit 14 can be three or more. In this case, the coils L3 andL4 are arranged, respectively, near the capacitors C1 and C3 asdescribed above and the other coils is/are arranged between the thesecoils L3 and L4.

Moreover, a capacitor may be inserted instead of the coils. Although thecapacitors C1, C2 and C3 are employed as the RF couplers, a directionalcoupler without a capacitor can also be employed.

Within the scope of the entire disclosure (including the claims) of thepresent invention, and based further on the basic technological idea,the preferred modes can be changed and adjusted. Moreover, variouscombination or selection from the various elements disclosed within thescope of the claims of the present invention.

1. A transmitter comprising: a first transmitting circuit which corresponds to a signal of a first frequency band; a second transmitting circuit which corresponds to a signal of a second frequency band; having a lower frequency band than the first frequency band; a first coupler which, disposed on an output signal line of the first transmitting circuit, branches and outputs part of an output signal from the first transmitting circuit; a second coupler which, disposed on an output line of the second transmitting circuit, branches and outputs part of an output signal from the second transmitting circuit; and a detector circuit detecting an input signal whose input terminal is coupled to a branched output terminal of the first coupler and a branched output terminal of the second coupler, wherein a first filter circuit which, arranged between the input terminal and the branched output terminal of the first coupler, passes a signal of the first frequency band, and a second filter circuit which, arranged between the input terminal and the branched output terminal of the second coupler, passes a signal of the second frequency band.
 2. The transmitter of claim 1, wherein said filter circuit comprises a series of coils arranged between said input terminal and said branched output terminal of the second coupler.
 3. The transmitter of claim 2, wherein the first coupler comprises a first capacitor whose first terminal is coupled to an output signal line of the first transmitting circuit and second terminal is coupled to the input terminal; the second coupler is a second capacitor whose first terminal is connected to an output signal line of the second transmitting circuit; a first coil of the coils, whose first terminal is connected to said input terminal, is disposed near the first capacitor; and a second coil of the coils, whose first terminal is connected to a second terminal of the first coil and second terminal is connected to a second terminal of the second capacitor, is disposed near the second capacitor.
 4. The transmitter of claim 2, wherein the coil is substituted by a capacitor.
 5. The transmitter of claim 1, further comprising: a third transmitting circuit which corresponds to signals of a third frequency band having a lower frequency band than the second frequency band; and a third coupler which, disposed on an output signal line of the third transmitting circuit, branches and outputs part of an output signal from the third transmitting circuit, wherein a filter circuit which, arranged between the input terminal and a branched output terminal of the third coupler, selectively passes a signal of the third frequency band.
 6. A transmitter comprising: a first transmitting circuit which corresponds to a signal of a first frequency band; a second transmitting circuit which corresponds to a signal of a second frequency band having a lower frequency band than the first frequency band; a first coupler which, disposed on an output signal line of the first transmitting circuit, branches and outputs part of an output signal from the first transmitting circuit; a second coupler which, disposed on an output line of the second transmitting circuit, branches and outputs part of an output signal from the second transmitting circuit; and a detector circuit detecting an input signal whose input terminal is coupled to a branched output terminal of the first coupler and a branched output terminal of the second coupler, wherein said input terminal is directly connected to the branched output terminal of the first coupler; and a phase shifter, providing a signal of the first frequency band with a larger phase shift than that for a signal of the second frequency band, is arranged between said input terminal and said branched output terminal of the second coupler.
 7. The transmitter of claim 1, further comprising a controller which variably controls a gain of a variable gain amplifier in the first transmitting circuit based on a detection output of the detector circuit while the first transmitting circuit operates and variably controls a gain of a variable gain amplifier in the second transmitting circuit based on a detection output of the detector circuit while the second transmitting circuit operates.
 8. A transmitter comprising: a first transmitting circuit which corresponds to a signal of a first frequency band; a second transmitting circuit which corresponds to a signal of a second frequency band having a lower frequency band than the first frequency band; a detector circuit which detects an input signal; a first coupler which, disposed on an output signal line of the first transmitting circuit, branches and outputs part of an output signal from the first transmitting circuit to the detector circuit; and a second coupler which, disposed on an output line of the second transmitting circuit, branches and outputs part of an output signal from the second transmitting circuit to the detector circuit; and the transmitter further comprising, between the second coupler and the detector circuit, one of a filter circuit which selectively passes a signal of the second frequency band and a phase shifter which provides a signal of the first frequency band with a larger phase shift than that for a signal of the second frequency band.
 9. The transmitter of claim 8, further comprising: a third transmitting circuit which corresponds to signals of a third frequency band having a lower frequency band than the second frequency band; and a third coupler which branches part of an output signal of the third transmitting circuit in an output signal line of the third transmitting circuit and outputs the part to the detector circuit, and a second filter circuit which, arranged between the second coupler and the detector circuit, selectively passes a signal of the third frequency band.
 10. The transmitter of claim 8, wherein both of the filter circuits comprise a coil or a series of coils.
 11. The transmitter of claim 8, wherein both of the filter circuits comprise a capacitor.
 12. The transmitter of claim 8, wherein both of the first coupler and the second coupler are a capacitor.
 13. The transmitter of claim 8, further comprising a controller which variably controls a gain of a variable amplifier in the first transmitting circuit based on a detection output of the detector circuit while the first transmitting circuit operates and variably controls a gain of a variable gain amplifier in the second transmitting circuit based on a detection output of the detector circuit while the second transmitting circuit operates. 